at the time when/that
2个回答

这个得看具体情况来确定.

1 如果定语从句中不缺少主语、宾语或表语,选择when

eg He came back home at the time when we were having dinner.

2 如果定语从句中缺少主语、宾语或表语,选择that

eg He came back home at the time that we chose..